This invention relates generally to printed circuit cards used in a control system and more particularly, to printed circuit cards used within a nuclear reactor protection system.
The generation of electrical power in a nuclear power plant is a complex process. Numerous parameters (such as, without limitation, pressure, temperature, flow, radiation level, valve position, pump status, etc.) must be constantly monitored and measured. These measurements are used by plant operators to regulate the process (e.g., actuate valves, pumps, control rod drive mechanisms, etc.), monitor the process (e.g., monitor tank levels, flows, temperatures, etc.), and provide protection to the equipment used within the process (e.g., prevent low coolant levels, overheating, over pressurization, etc.; trigger a reactor “trip”, a unit runback; etc.).
In the case of a nuclear power plant, the protection function, in particular, is very demanding. Thus, nuclear power plants employ a nuclear reactor protection system. To increase reliability of the protection system, redundant sets of critical sensors are provided to measure the numerous process parameters. For instance, four redundant sets of sensors are typically employed to measure a critical parameter, such as reactor core temperature. The sensors may be divided into a number of data channels which are in communication with the nuclear power plant's protection system. If one sensor fails, the three remaining sensors are available to measure the reactor core temperature. To prevent an unintended interruption of normal operations, the signals produced by the redundant sensors are correlated before initiating an emergency or safety response. In the current example, for instance, an indication by at least two out of the four sensors may be required as a prerequisite to actuating an emergency or safety response to lower the reactor core temperature.
Many protection systems employed today are Solid State Protection Systems (“SSPS”) which employ discrete digital electronics, mechanical switches, and electromechanical relays, among others. The components of the SSPS are typically arranged in redundant logic “trains” which insures, for example, that the reactor does not inadvertently trip due to a component failure in a single logic train. Instead, the second logic train maintains the proper control. More specifically, if one logic train is off-line, malfunctioning, etc., the other train is able to provide the necessary protection. Examples of protection systems can be found in commonly assigned U.S. Pat. Nos. 6,062,412 issued to Stucker et al., 4,804,515 issued to Crew et al., and 4,399,095 issued to Morris.
Each logic train of the SSPS typically includes a number of printed circuit cards which are used, for example and without limitation, to check the correlation between redundant sensors, check for under-voltage conditions, check for over-voltage conditions, etc. Each train may include, for example and without limitation, thirty-five (35) Universal Logic cards, one (1) Undervoltage Driver card (UV Card), and four (4) Safeguard Driver Cards.
Most existing printed circuit cards, however, employ dated technology. Existing printed circuit cards, for example, operate from a 15 volt power supply and thus consume large amounts of power. Additionally, most existing printed circuit cards do not have adequate indicators (such as LED's) incorporated therein to convey the current status of the card, the inputs/outputs, etc. As a result, troubleshooting of the SPSS is difficult. Generally, the existing printed circuit cards must be periodically tested by taking a single train out of service (i.e., taking it off-line). Once off-line, a series of test pulses are applied to the inputs of the off-line train to test the printed circuit cards in that train; the second train remains on-line and provides protection to the nuclear power plant. After testing is completed, the first train is placed back on-line. Next the second train is taken off-line and a series of test pulses are applied to the inputs of the second train to test its printed circuit cards; the first train remains on-line and provides protection to the nuclear power plant. After testing is completed, the second train in placed back on-line.
Under a typical test protocol, the trains are alternatingly tested every three to six months. For example, train-1 is tested in January, train-2 is tested in April, train-1 is tested in July, and train-2 is tested in October. As is evident, each train only undergoes testing once every six months. Thus, a malfunction that occurs shortly after a train is tested may not be discovered until the next scheduled test for that train (e.g., six months later; or even worse, only discovered after the train has caused an inadvertent reactor trip). Newer protection systems may be available; however, a wholesale change out of the protection system is cost prohibitive and complicated.
Consequently, there is a need in the art for an improved printed circuit cards for an existing SSPS. More particularly, there is a need in the art for improved printed circuit cards that provide high reliability, low power consumption, which may be incorporated as a direct replacement to existing cards, and which provides continuous self-testing, among others.